Trachoma is the leading infectious cause of blindness worldwide. Current efforts at trachoma control by mass treatment of communities with topical antibiotics have little sustainable effect. A new oral antibiotic, Azithromycin, offers a potentially long-lasting effect on the community pool of chlamydia infection. The goal of this project is to determine the impact of Azithromycin on chlamydial infection and clinical trachoma over time in three diverse settings where trachoma is endemic. Two communities in Tanzania, Egypt, and Gambia will be randomized to Azithromycin or topical tetracycline and followed at regular intervals for 22 months. Rates of re-emergent ocular infection and patterns of clinical disease in each setting will be documented over time. The risk of re-emergent infection associated with nasopharyngeal carriage of chlamydia, migration of infected persons into the village, and known risk factors for transmission of trachoma will be determined. The potential use of Azithromycin for community control of trachoma clearly depends on the timing, magnitude, and likely sources of re-emergent infection in comparison with standard topical treatment. This project represents a unique opportunity to provide key data on the effectiveness over time of mass treatment and high risk groups to monitor as likely sources of re- infection.